I have a 1991 Mustang with a 302. As of late, the car has been hard to crank over (the starter is very slow to spin but the car still cranks over) . The battery is only 6 months old and I replaced both battery cables. Just the other day I found the car to be completely dead. The battery voltage only read 7.5 Volts with a multimeter. I took the battery in for service and the retailer charged the battery and said it checked out fine.
After reinstalling the battery the car started fine. One day later, I found the battery to be low again. I jump started the car and drove it around. I checked voltage when the car was running it read 11.7 VDC. With the car running and all accessories turned off, I disconnected the negative battery cable to see if the car would continue to run on the alternator; the car immediately died.
I suspect the 120K miles have taken a toll on the starter, but now I also believe I have a problem with a voltage regulator and/or alternator. Any words of advice? Jeff
I think I agree with you, but before you do anything to the starter, I would get a complete charging system test done ON the car,
1. Load test battery
2. Check alternator output
3. Check for voltage drain – something left on with the engine off that is draining the battery
4. Check starter amp draw
At first glance I would suspect a weak alternator, but disconnecting the battery cable with the engine running is not a good test for a computer controlled vehicle. I would want to rule out the possibility of a voltage drain somewhere first, so I highly recommend finding a competent electrical shop in your area for the test…and if needed let them overhaul the alternator and the starter for you.
Austin C. Davis